1. Field of the Invention
The present invention relates to a liquid supply device adapted to supply liquid by an increase or decrease of a pump internal volume, and an image forming apparatus including the liquid supply device.
2. Description of the Related Art
Conventionally, a liquid supply device adapted to supply liquid by an increase or decrease of a pump internal volume utilizes a diaphragm pump including a diaphragm, a first check valve, and a second check valve, and the diaphragm being formed of an elastically deformable material to change the pump internal volume. The diaphragm pump includes a compression coil spring provided therein to actuate the diaphragm outward. The diaphragm pump further includes a pressing member provided to press the diaphragm from the outside toward the center of the diaphragm against the actuation force of the compression coil spring.
In the diaphragm pump, a volume of the diaphragm is decreased by pressing the diaphragm using the pressing member, so that liquid is ejected via the first check valve. By releasing the pressing member from the diaphragm, an internal pressure of the diaphragm is reduced due to the outward actuation force of the spring provided in the diaphragm, so that liquid is attracted via the second check valve. This diaphragm pump is commonly used in an inkjet recording apparatus as an ink supply unit to supply ink (liquid) from an ink tank (main tank) to a head tank (sub-tank).
For example, Japanese Patent No. 3797548 discloses an inkjet recording apparatus. In this inkjet recording apparatus, an ink tank and a head tank are connected to each other via an ink passage, and the ink passage is formed into an enclosed passage to which a diaphragm pump is connected. The inkjet recording apparatus includes plural recording heads each ejecting ink from the head tank. Each of the recording heads includes an ink tank, a diaphragm pump, a head tank, and an ink passage. The inkjet recording apparatus includes a pump drive device adapted to select one of the diaphragm pumps as a target diaphragm pump and drive the selected diaphragm pump. This pump drive device uses, as a pump drive source, a drive motor having a rotating shaft which is rotatable in forward and backward directions and is selectively connected to and drives the target diaphragm pump. The diaphragm pumps are disposed along a peripheral surface of the rotating shaft and arranged in a line substantially parallel to an axial direction of the rotating shaft.
FIGS. 16A to 16D are diagrams for explaining the operation of a pump drive device 400 disclosed in Japanese Patent No. 3797548. As shown in FIGS. 16A to 16D, the pump drive device 400 includes a first link 402 and a second link 403 for each of the diaphragm pumps. The first link 402 includes a first tooth portion 401 with plural teeth formed at an edge of an end portion of the first link 402. The second link 403 is adapted to change the volume of the diaphragm pump due to an up/down movement of the second link 403 caused by engagement with the first link 402. The first link 402 is rotatably supported on the device and disposed to face a peripheral surface of a rotating shaft 404 of a drive motor, and supporting shafts of the first link 402 are arranged in parallel with an axial direction of the rotating shaft. The second link 403 includes a pressing member 406 adapted to press a diaphragm 405 in a contraction direction of the diaphragm 405, and an end portion of the second link 403 is movably connected to an end portion of the first link 402 which is opposite to the end portion thereof where the first tooth portion 401 is formed. The second link 403 is subject to an up/down movement in a direction indicated by the arrow C or the arrow F in FIGS. 16A to 16D while the movement of the second link 403 is regulated by a pin 403a. Moreover, the second link 403 is actuated by a compression coil spring (first spring) 407 in a direction to approach the diaphragm 405. The pressing member 406 of the second link 403 presses the diaphragm 405 such that ink is not extruded from the diaphragm 405 by the actuation force of the first spring 407. A second tooth portion 408 with plural teeth is formed on the peripheral surface of the rotating shaft 404 of the drive motor, and the teeth of the second tooth portion 408 are selectively engaged with the teeth of the first tooth portion 401 of the first link 402. The second tooth portion 408 is disposed on the peripheral surface of the rotating shaft 404 of the drive motor in a position in the circumferential direction to face the first tooth portion 401. When viewed from the axial direction of the rotating shaft 404, the second tooth portions 408 of the diaphragm pumps are arranged in the positions at mutually different phase angles. A compression coil spring (second spring) 409 is provided within the diaphragm 405 to actuate the diaphragm 405 outward.
In the above-described pump drive device 400, a selection operation is performed to select one of the diaphragm pumps 410 as a target diaphragm pump, and a drive operation is performed to drive the target diaphragm pump 410 so as to supply ink.
Here, a state of the pump drive device 400 in which the first tooth portion 401 and the second tooth portion 408 are not engaged with each other is referred to as an “initial state”. In the initial state of the pump drive device 400, rotation of the rotating shaft 404 is started in the direction indicated by the arrow A in FIG. 16A. The rotating shaft 404 is rotated until the first link 402 corresponding to the target diaphragm pump 410 is engaged with the first tooth portion 401. Rotation of the first link 402 which is engaged with the first tooth portion 401 is started in the direction indicated by the arrow B in FIG. 16A, and actuation of the second link 403 is started in the direction indicated by the arrow C in FIG. 16A. If the rotating shaft 404 is further rotated in the direction indicated by the arrow A in FIG. 16A, the first link 402 is further rotated in the direction indicated by the arrow B in FIG. 16A and the second link 403 is further actuated in the direction indicated by the arrow C in FIG. 16A. By this actuation, the second link 403 is actuated in the direction indicated by the arrow C in FIG. 16B. If the first tooth portion 401 of the first link 402 with which the second tooth portion 408 of the rotating shaft 404 is engaged does not correspond to the target diaphragm 405, the rotation of the rotating shaft 404 in the direction indicated by the arrow A in FIG. 16B is continued until the second tooth portion 408 of the rotating shaft 404 is engaged with the first tooth portion 401 of the first link 402 corresponding to the target diaphragm 405. This operation causes the target diaphragm 405 to be selected.
After the target diaphragm 405 is selected, if the rotating shaft 404 is rotated in the direction indicated by the arrow D in FIG. 16C, rotation of the first link 402 is started in the direction indicated by the arrow E in FIG. 16C and actuation of the second link 403 is started in the direction indicated by the arrow F in FIG. 16C. If the rotating shaft 404 in this state is further rotated in the direction indicated by the arrow D in FIG. 16C, the first link 402 is further rotated in the direction indicated by the arrow E in FIG. 16C and the second link 403 is further actuated in the direction indicated by the arrow F in FIG. 16C. By this actuation, the pressing member 406 of the second link 403 presses the diaphragm 405 in the contracting direction of the diaphragm 405 while resisting the force of the second spring 409. Hence, the volume of the diaphragm 405 is reduced and the ink in the diaphragm 405 is supplied to the head tank (not illustrated). If the rotating shaft 404 in this state is rotated in the direction indicated by the arrow A in FIG. 16A, the first link 402 is rotated in the direction indicated by the arrow B in FIG. 16A and the second link 403 is actuated in the direction indicated by the arrow C in FIG. 16A. By this actuation, the pressing member 406 of the second link 403 is moved and no longer presses the diaphragm 405, and the volume of the diaphragm 405 is increased according to the actuation force of the first spring 407. This operation may attract ink in the ink tank (not illustrated) into the diaphragm 405.
Incidentally, if the rotating shaft 404 is rotated in the direction indicated by the arrow D in FIG. 16C until the engagement between the second tooth portion 408 of the rotating shaft 404 and the first tooth portion 401 of the first link 402 is cancelled, the target diaphragm may be changed to another diaphragm or the pump drive device 400 may be set in the initial state. In this initial state, the pressing member 406 of the second link 403 presses the diaphragm 405 lightly such that ink is not extruded from the diaphragm 405 by the actuation force of the first spring 407.
However, in the pump drive device disclosed in Japanese Patent No. 3797548, the diaphragm 405 tends to be increased in the volume due to the use of the second spring 409 provided in the diaphragm 405 to actuate the diaphragm 405 outward. If the volume of the diaphragm 405 is decreased with the consumption of ink, the internal space of the diaphragm 405 is subject to negative pressure. In such a condition, the increase in the volume of the diaphragm 405 by the actuation force of the second spring 409 is not regulated. For example, if the ink tank is removed and the diaphragm 405 is opened to the atmosphere when the second link 403 is moved downward as shown in FIG. 16B or when the rotating shaft 404 is in the initial position, it is likely that external air is attracted into the diaphragm 405. For example, if the second tooth portion 408 of the rotating shaft 404 associated with the target diaphragm corresponding to the ink tank to be removed should be engaged with the first tooth portion 401 of the first link 402 and the target diaphragm should be pressed by the pressing member of the second link as shown in FIGS. 16A, 16C and 16D in the above-mentioned condition in order to regulate the increase in the volume of the diaphragm 405, external air may not be attracted into the diaphragm even when the ink tank is removed.
However, the liquid supply device disclosed in Japanese Patent No. 3797548 is arranged so that only the target diaphragm among the plural diaphragms 405 is pressed by the pressing member of the second link. If an ink tank corresponding to another diaphragm 405 in which the increase in the volume is not regulated is removed erroneously, external air enters that diaphragm. The air once introduced in the wrong diaphragm cannot be ejected from the side of the ink tank where the first check valve is disposed. The air introduced in the wrong diaphragm must be ejected from the side of the recording head together with ink. As a result, the ink used to eject the air in this manner will be wasted unnecessarily.